The 3GPP (The Third Generation Partnership Project) which is one of standardization organizations has almost completed the standardization of 3GPP LTE (Long Term Evolution) Rel-10 (systems developed after this may be referred to as LTE-A (LTE Advanced)) which is one of the fourth-generation mobile communication systems, and is currently standardizing LTE Rel-11 which is obtained by enhancing Rel-10.
In carrier aggregation (CA) which is a key technique for improving a transmission speed after Rel-10, multiple LTE carriers called component carriers (CCs) are used at the same time for communication, achieving broadband transmission with a bandwidth exceeding 20 MHz.
For the uplink (communication from a terminal (which may be referred to as a user equipment (UE), a mobile station apparatus, or a wireless terminal) to a base station) of LTE Rel-11, a study is progressing for a heterogeneous network in which a macro base station (evolved Node B (eNB)) forming a macro cell (macro area) covering an area equivalent to that of a cellular system of the related art and an LPN (a low power node which may be also referred to as a radio remote head (RRH)) forming a small cell covering a narrow area in the macro cell are disposed. In the heterogeneous network, the macro base station and the LPN which serve as independent cells utilize radio resources, whereby cell-splitting gain (area-splitting gain) may be obtained.
The study for Rel-12 which is the succeeding standard of Rel-11 has been also started. Transmission in a small cell using a carrier frequency which is different from that in a macro cell is being studied (for example, NPL 1). In this case, the macro base station may offload the data traffic to the small cell. Therefore, a macro base station instructs a terminal which needs high-speed data transmission to be connected to an LPN, whereby traffic may be offloaded, and throughput (capacity) in the macro cell constituted by the macro base station and the LPN may be increased. Using the CA technique described above, specification of dual connectivity in which, while a connection to a macro cell is established, a connection to a small cell is established by using a different CC at the same time is being studied (for example, NPL 2).